1. Field of the Invention
The invention relates to the field of optical receivers and transceivers capable of operating at multiple data rates, and preferably having autonegotiation capabilities.
2. Background Information
Currently, standards are being developed for relatively high-speed multi-Giga-bit-per second (Gb/s) optical links. However, optical transceiver users may require future transceivers to inter-operate with lower-speed ‘legacy’ transceivers. Therefore, future optical transceivers should be capable of operating at different speeds. Ideally, an optical transceiver should either be capable of internally detecting the operating bit-rate (also referred to as operating speed or signaling rate herein) of the signal that is presented to it, or have an external input that provides information on the link operating speed. Further, based upon the determined operating bit-rate, the transceiver should be able to dynamically change the characteristics of either its transmitter or receiver, or both, in order to produce a functional, standard-compliant link at the proper signaling rate.
The ability to dynamically detect the operating bit-rate and adjust the transmission and reception of a transceiver to match the detected rate is sometimes referred to as “autonegotiation.”
In addition, it is desirable that the functionality of the optical transceiver be independent of the physical form-factor of the transceiver and, therefore, the transceiver should be able to be implemented in any physical package, i.e., GBIC (GigaBit Interface Converter), Small-Form-Factor, 1×9, etc., in addition to be available in fixed or hot-pluggable variants.
If the optical transceivers currently under development were able to inter-operate with other transceivers already in use that have been designed for different signaling rates, then this would allow users to continue to operate the large base of installed optical transceivers and upgrade to higher performance transceivers without making the ‘legacy’ devices obsolete. An optical transceiver that is capable of operation with such functionality could be inserted into an optical link operating at any speed and be able to adapt its performance to match the requirements of the link.
However, the ability to inter-operate with legacy transceivers is a feature that has not previously been achieved in successive generations of optical transceivers. That is, the problem of producing an optical transceiver capable of standard-compliant operation at multiple bit-rates has not previously been overcome. One technical challenge is implementing a receiver front-end design (photodetector and transimpedance amplifier) that is capable of dynamic bandwidth modification. Therefore, an optical transceiver that is designed to operate at multiple data rates would require an optical receiver whose bandwidth can be dynamically modified.
For example, currently optical transceivers are being developed that will operate at the double-speed Fibre Channel (FC) bit-rate of 2.125 Gb/s. However, already installed ‘legacy’ transceivers operate at a bit-rate of 1.0625 Gb/s. Therefore, transceivers which are able to inter-operate with legacy full-speed FC transceivers that work at a bit-rate of 1.0625 Gb/s would be, desirable. That is, it would be desirable to produce a transceiver that is capable of operation in compliance with the double-speed Fibre Channel standard at 2.125 Gb/s and the legacy full-speed FC standard of 1.0625 Gb/s. Such a transceiver would allow users to upgrade the capacity of their optical data links without making legacy components obsolete. Transceivers with this functionality could be applicable to Gigabit Ethernet, Fibre Channel, Infiniband, ATM, and SONET networks, along with future optical networking standards that are developed.
However, a problem that arises in achieving the desired interoperability between these two generations of transceivers, for example, is that the 1.0625 Gb/s FC specification imposes a maximum receiver bandwidth limit of 1.5 GHz. The conventional rule of thumb is that for 2.125 Gb/s operation, a receiver bandwidth of 1.6 GHz is required. Therefore, compliance with the 1.0625 Gb/s standard and the ability to operate at 2.125 GB/s impose conflicting requirements on the receiver bandwidth of the optical transceivers. In order to produce a transceiver that is capable of working at both signaling rates, the bandwidth of the receiver must be switchable.
Therefore, there is a need for an optical transceiver that has the ability to adapt the receiver bandwidth to that required for the link operating speed. In particular, a receiver capable of operating at both the lower or lowest speed, and the higher or highest speed, should be able to adjust its bandwidth to comply with the maximum bandwidth allowed by the respective speed standard. It would also be desirable if the receiver had the ability to detect link operating speed dynamically thereby fully realizing autonegotiation capabilities.
Although the FC signaling rates of 2.125 Gb/s and 1.0625 Gb/s were used as an example above, the general methodology needed for controlling receiver bandwidth is equally applicable to different operating bit-rates and other optical networking standards. Further, it should be apparent that the need is not necessarily limited to a receiver capable of operating at just two different bit-rates, but is applicable to a receiver capable of operating at two or more different selectable bit-rates.
IBM Technical Disclosure Bulletin (TDB) Vol. 37, No. 10 (October 1994) at page 69 describes a “Filter Method to use Self-Pulsating Lasers at Gigabit Data Rates.” IBM TDB Vol. 37, No. 12 (Dec. 1994) at page 301 describes an “Adjustable Bandwidth Hybrid Receiver.”
Therefore, it is apparent that a switchable-bandwidth receiver capable of operating at multiple bit rates and making it possible to implement the functionality of link-speed autonegotiation in future optical data links is needed. In addition, methodologies for dynamically controlling the optical receiver's bandwidth should be independent of the physical form-factor of the transceiver. The methodologies should also be applicable to both single-ended and differential optical receiver designs.
Therefore, a need exists for a switchable-bandwidth optical receiver.